Intracranial pressure (ICP) is measured for the diagnosis and the management of disorders such as hydrocephalus and pseudotumor cerebri. ICP is often measured following serious head injury, stroke edema, and intracranial hemorrhage, and is also of value in the management of certain neurological or ophthalmic diseases that are associated with increased cerebral pressure.
The current standard of care to measure ICP involves surgically inserting a sensor into the cranium through an access hole drilled through the skull. Present treatment techniques for monitoring ICP or managing intracranial hypertension (ICH) generally require invasive placement of subarachnoid bolts, counter-pressure epidural devices (Ladd or Camino fiber-optic monitors) or intra-ventricular catheters coupled to external pressure monitors. Such surgical procedures carry the risk of complications including infections, hemorrhage, herniation, damage to nervous tissue, and death, and are very expensive. In addition, cerebrospinal fluid pressure may be altered the instant the measurement is performed as a result of leakage of cerebrospinal fluid. Despite the risks, invasive measurements of ICP are nonetheless commonplace, as they provide a treatment option in addition to a diagnostic option, which non-invasive devices cannot.
Because of these risks, ICP is only measured in patients who are critically ill and is not a practical solution for assessing the severity of a patient's injury or in triage. Accordingly, there is a need for non-invasive, momentary assessment of ICP in certain acute situations such as patients with acute shunt obstruction, in the neuro-intensive care unit (NICU) when lumbar puncture is not practical, in the emergency room or by emergency medical technicians (EMT) and other civilian and military first-responders in response to head injury or the like.
Existing attempts to accurately and non-invasively determine ICP are not optimal, as such approaches do not provide a reliable measure of ICP. Individual baseline variability due in part to anatomical variances further limits the application of these methods. Additionally, these methods have demonstrated insufficient precision when compared to invasive ICP monitors. Accordingly, there is an unmet need in the art for easy to use, portable and inexpensive devices and methods capable of non-invasive determination of intracranial pressure.
Part of a routine neurologic assessment in patients with a head injury or when elevated ICP is suspected is the pupillary reflex examination. The pupillary reflex is the response of the pupil to light and can provide valuable information about the degree or progression of brain injury. It has been shown that patients with an abnormal pupil response also have significantly higher ICP than patients with normal pupillary activity.
Traditionally, the pupillary reflex has been subjective and determined by waving a flashlight into a patient's eye to observe the pupil's reactivity and thus the status of the nervous system and brain. Devices to quantitatively assessed changes in constriction and dilatation of pupils in response to light also exist. Such devices are expensive, serve the single function, require additional training and are not integrated into a system for determining ICP.
Accordingly, there is an unmet need in the art for a method and integrated instrument to measure, in a virtually simultaneous or sequential manner, a spectrum of neurological and neuro-ophthalmic indicators such as ICP, ophthalmodynamometry (ODM), IOP, pupillary reflex and other similar functions. Such an instrument would significantly enhance the available information to assess the neurological status of the patient.
In addition to the patient conditions summarized above in which an assessment of ICP is desirable, the field would also benefit from devices and methods capable of providing a more accurate diagnosis of glaucoma. Traditionally, a patient's intraocular pressure (IOP) has been to the single most important metric that determines a patient's susceptibility to glaucoma. Knowledge of a patient's ICP in addition to a patient's IOP will provide the clinician with the translaminar pressure (i.e., the pressure difference between IOP and ICP that is applied to the optic nerve head), which may be a more accurate indicator of glaucoma susceptibility than IOP alone.